Study On The Effect Of Ac-SDKP On Apoptosis Of Alveolar Epithelial Cells In Pulmonary Fibrosis Model In Mice

Objective:To investigate the effect of Ac-SDKP on apoptosis in the course of idiopathic pulmonary fibrosis（IPF）and to explore the related mechanism of action by using bleomycin-induced pulmonary fibrosis model in C57BL/6 mice.Methods:Twenty-four healthy male C57BL/6 mice（body weight 25±2g）were selected and divided into three groups according to the random number table method:blank control group（N group,n=8）,pulmonary fibrosis model group（B）Group,n=8),Ac-SDKP interventional treatment of pulmonary fibrosis group（H group,n=8）.Mice in groups B and H were treated with intratracheal instillation of bleomycin（5 mg/kg dissolved in 0.9%physiological saline and formulated in a mixture of 50μl）to establish a mouse pulmonary fibrosis model 14 days after injection.Ac-SDKP micro-release pump(Ac-SDKP mixed solution:Ac-SDKP 800 ug.kg^-1.d^-1,glacial acetic acid 0.1 M,captopril 100 mg)was embedded in the abdominal cavity of Group H mice..kg^-1.d^-1,),continuous intervention for 14 days.The N-group modeling method was the same as that of group B,intratracheal instillation of bleomycin and the same volume（50μl）of 0.9%sodium chloride saline.All mice were sacrificed on the 28th day after completion of the model by abdominal aorta phlebotomy and lung tissues were taken.The degree of pathological changes in lung fibrosis was observed and scored by HE staining and Masson staining.Hydroxyproline（HYP）content in lung tissue was measured by alkali hydrolysis method to determine whether pulmonary fibrosis model was successfully prepared,and lung fibrosis severity was evaluated.Immunohistochemistry was used to observe the expression of GRP78,CHOP,Bax and AIF proteins.The expression of apoptosis-inducing factors AIF and Caspase 3 mRNA was detected by fluorescent RT-PCR.The TUNEL method was used to detect the apoptosis of mouse lung tissue.Results:The pulmonary fibrosis in the model group was significantly aggravated,and the application of Ac-SDKP reduced pulmonary fibrosis.The expression of CHOP and GRP78in the model group was extensive.Compared with the model group,the treatment group was inhibited and the Bax expression was inhibited（P<0.05）.The m RNA of the mitochondrial apoptosis marker AIF and caspase3 in the treatment group was lower than that in the model group,and the difference was statistically significant（P<0.05）.The alveolar epithelial cell death index in the treatment group and the model group was significantly higher than that in the control group,and the difference between the groups was statistically significant（P<0.05）.Conclusion:Ac-SDKP may reduce the apoptosis of pulmonary fibrosis cells through the ERS-mitochondrial pathway in the pathological process of idiopathic pulmonary fibrosis.